(a) Field of the Invention
The present invention relates to a high performance large aperture ratio telephoto lens system having a focal length of 200 mm to 300 mm.
(b) Description of the Prior Art
The conventional telephoto lens systems having focal lengths of 200 mm to 300 mm were generally designed for aperture ratios on the order of F4 or F2.8 at best. In the recent trend, however, interchangeable lenses for cameras of 35 mm size film are designed for larger aperture ratios and development of telephoto lens systems having larger aperture ratio are desired. In designing a telephoto lens system having a larger aperture ratio, the greatest problems lie in the difficulty to correct chromatic aberration due to secondary spectrum, difficulty to correct spherical aberration and Petzval's sum at the same time, and to prevent total length of the lens system from being prolonged remarkably. For this reason, the telephoto lens system having an aperture ratio on the order of F2.0 is only the one disclosed by Unexamined Published Japanese Patent Application No. 134425/78. This lens system and other conventional examples have large telephoto ratios around 1.2 and large Petzval's sums ##EQU1## around 0.2.